This invention relates to fans of the type that are used in automotive vehicles for drawing air through radiators, particularly, clutch fans. The invention involves an improvement to the blades of such fans resulting in quieter and more efficient operation.
Clutch fans are employed in vehicles in which the engines are mounted in the "north-south" direction. The fan is mounted on an external portion of the engine water pump's shaft via a clutch. The size or capability of the clutch is determined by the input speed of the water pump, generally 1.25 times the engine rpm, and the torque of the clutch fan. Generally, the airflow required for cooling the vehicle determines the torque of the fan if the fan is properly designed.
Conventional bladed clutch fans can best be described as having a certain number of blades, commonly five or seven, of radial (non-skewed) blade profile. The material of the blades may be either steel or aluminum or plastic. These fans have in the past been used for their cooling performance at the expense of fan noise, even though the noise level has been considered acceptable.
With the present invention, the required cooling performance can be achieved, or even improved, while the sound pressure levels generated by the fan can be significantly attenuated. Moreover, the fan torque is reduced, allowing the clutch size to be decreased so that a cost saving can be realized.
A fan blade constructed according to general principles of the invention comprises: a varying skew leading edge that has inner, intermediate, and outer regions such that the intermediate region is of increasing skew in the direction of rotation and the outer region is of decreasing skew; the pitch ratio increases as a function of increasing blade radius; and along the outer region of the leading edge, the blade increases in pitch on a defined curvature as a function of blade radius and angle to form a tip curl.
Features, advantages, and benefits of the invention will be seen in the ensuing description, claims, and accompanying drawings which disclose a presently preferred embodiment according to the best mode contemplated at the present time in carrying out the invention.